Increased usage of renewable energy sources such as solar radiation is important in reducing dependence upon foreign sources of oil and decreasing green house gases. Devices have been developed in the past that track the motion of the Sun to re-direct and concentrate incident solar radiation. FIG. 1 illustrates one example of a prior art device that utilizes a parabolic dish mirror 10 with a central axis 12 that is pointed generally toward the Sun 14. Incident solar radiation 22 is received and reflected by the parabolic dish mirror 10 and concentrated at its focus 16, where a thermal target (not illustrated) can be mounted so that it can be heated. The parabolic dish mirror 10 is supported for independent movement by a two-axis tracking support 18 mounted atop a supporting structure 20 such as a tower. Optical encoders (not illustrated) associated with the tracking support 18 provide signals indicative of the direction and amount of rotation of the parabolic dish mirror 10 so that motor drives and a control system (not illustrated) can be used to track the Sun and increase the efficiency of the energy transfer.
FIG. 2 illustrates another example of a prior art device similar to the device of FIG. 1 except that the device of FIG. 2 utilizes a parabolic trough mirror 30. Dashed line 32 illustrates a common plane of the focal line 36 of the parabolic trough mirror 30 and the Sun 14. A single axis tracking support 38 carries the parabolic trough mirror 30 and is mounted atop a tower 40. Incident light rays from the Sun such as 42 are collected and reflected by the parabolic trough mirror 30 and concentrated on a pipe (not illustrated) that extends along the focal line 36. This allows a heat transfer fluid such as water or liquid sodium to be heated. The heating efficiency can be improved by mechanisms (not illustrated) that cause the parabolic trough mirror 30 to pivot and track the Sun.
FIG. 3 illustrates another prior art device that utilizes a heliostat flat mirror 50 that receives incident light rays 52 from the Sun 14 and reflects them against a thermal target 58 atop a tower 59. Another tower 54 carries a two-axis tracking support 56 which supports a flat mirror 50. Drive and control mechanisms (not illustrated) allow the flat mirror 50 to be independently moved about a rotate axis 60 (azimuth) and about a tilt axis 62 (elevation) to ensure that the Sun's rays are reflected onto the target 58 as the Sun moves across the sky.
There are many variations of the foregoing devices, but to date, none has been widely adopted due to the complexity, reliability, accuracy and/or expense of the tracking mechanisms.